Refactor for cleanup

See merge request !468

should be an optimization, but has no real performance impact and prohibits SessionModel from refactoring

Harmonize UI - use collapsible group boxes as on many other spots in the UI

See merge request !467

...instead of accordion widget

Minor enhancement & cleanup & fix

See merge request !466

minor corrections, while cleaning up old edit scripts

See merge request !465

update devtools/lines_of_code

See merge request !464

Remove net oriented sample editor

See merge request !463

...which held the position of an item in the GraphicsScene of the net oriented sample editor

still no classes of the net oriented sample editors are removed, only the UI doesn't show it any more

simplify code; remove test code

See merge request !462

this was used as a playground to try out things

Improve layer editor

See merge request !461

Complete editors for interference

See merge request !460